Cyclopropane tricarboxylic acid ester lubricants



States This invention relates to synthetic ester lubricants and the method of their preparation. More particularly this invention is directed to esters of cyclopropane tricarboxylic acid.

The presently available mineral hydrocarbon lubricating oils now widely used in conventional internal combustion engines have limited application under the rigorous conditions at which jet engines operate. Conventional hydrocarbon oils generally are unstable at high temperatures and are readily oxidized to compounds unsuitable for lubrication. When such hydrocarbon lubricating oils have low pour point, they often contain volatile materials which are lost at high temperatures, thereby adversely affecting the lubricating properties of the oil.

These inherent disadvantages of hydrocarbon lubricating oils have generally made themunsuitable for jet and turbo-jet engines now used to power modern aircraft. In recent years a series of synthetic lubricants have become available to overcome some or" the disadvantages of hydrocarbon lubricating oils. These new synthetic lubricants are generally characterized by lower changes in viscosity at increasing temperatures, high stability to oxidation, low pour point, and high flash point.

It is accordingly an object of this invention to provide a new series of synthetic ester lubricants which overcome the inherent disadvantages of hydrocarbon lubricating oils.

It is another object of the present invention to provide a class of new compounds particularly suitable as lubricants for high temperature use.

It is another object of the present invention to provide new esters which are usable under lubricating conditions too rigorous for conventional mineral oil lubricants.

It is a still further object of the present invention to provide a series of new esters, namely cyclopropane tricarboxylic acid esters.

Other objects and advantages of the new compounds of the present invention, together with the methods by which they are made, will be readily apparent from the detailed description which follows.

The compounds of the present invention may be generally defined by the following structure.

wherein A and B are selected from the group consisting of H and COOR with the proviso that A is COOR when E is H and B is COOR when Ais H, and R is a straight or branched chain group having from 5 to 20 carbon atoms. The R radical may, of course, represent like or unlike groups depending on the reactant materials used in their preparation.

In preparing compounds of the foregoing structure a trimethyl or triethyl ester of cyclopropane tricarboxylic acid is first prepared. These esters may be prepared in several ways. For example, when preparing the 1,1,2 tri: carboxylic triethyl ester, one mol of ethyl A, B, dibromopropionate is reacted with an equimolar amount of ethyl malonate. The resulting triethyl ester is then reacted in QICIII 3,010,999 Patented Nov. 28, 1961 lCC in the initial reaction.

the manner hereafter described to provide the desired tri Having prepared the trimethyl or triethyl ester of the 1,1,2 or 1,1,3 tricarboxylic acids, the tri esters desired are obtained by reacting a selected monoalcohol or a mixture of monoalcohols with the trimethyl or triethyl ester under alcoholysis conditions (see Engineering Chemical Technology, Kirk and Othmer, vol. 5, p. 817). The monoalcohol or mixture of monoalcohols used will have at least 5 carbon atoms and preferably not more than 20 carbon atoms. The lower limit of 5 carbon atoms for the selected monoalcohol used is essential if the final product is to be used as a lubricant, since it has been found that tri esters in which the alcohol chain is less than 5 carbon atoms generally do not possess satisfactory lubricating properties. Having selected a mono-alcohol of suitable chain length, the latter is reacted in a molar excess preferably in a molar ratio of tri ester of the triacid to the selected alcohol of at least 1:10. When a single monoalcohol is used the fine tri ester product will be mixed unless complete alcoholysis is accomplished. If more than one monoalcohol is used e.g. two difierent alkanols are used such as is contemplated by the present inventors the final triester product will be mixed in structure type as well as degree depending on the completeness of alcoholysis.

In carrying out the alcoholysis reaction the following straight chain alcohols may be used: amyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, cetyl and heptadecyl alcohol. Among the branched chain alcohols which can be used are 2-ethylhexyl, 2,3-dimethylbutanol, 3- methylpentanol, methylisobutylcarbinol, Z-methylpentanol, 2,2-dimethylbutanol-3, Z-methylpentanol-Z, 3- methylpentanol-3, 2,3-dimethylbutanol-2, 2,4-dimethylpentanol-3, 4-1nethylhexanol-l, 2,3,3 trimethylbutanol-Z, methyl-n-hexylcarbinol and 2,2-dimethy-1pentanol. Other monoalcohols such as those which include an etheroxygen linkage may be used. Typical satisfactory alcohols of this type are ethylene glycol n-butyl ether, methyl Cellosolve, ethyl Cellosolve, butyl Cellosolve, l-butoxyethoxy-Z-p-ropanol, hexyl Cellosolve, methyl Carbitol, ethyl Carbitol, butyl Carbitol, methoxytriglycol, ethoxytriglycol and hexyl Carbitol.

Suitable also for use in the esterification of the triethyl or trimethyl esters of the 1,1,2 or 1,2,3 triesters are the alcohols obtained in the so-called Oxo process. The Oxo process is well known in the art and refers to a process in which an olefin feed is first reacted with carbon monoxide and hydrogen at a temperature between and 250 C. and at a pressure of about to 400 atmospheres in the presence of a cobalt or similar catalyst. The resulting aldehydes are then hydrogenated to form the desired alcohols. The alcohol products obtained will be of varying chain length, generally from about C to C in length.

The new triesters of the 1,1,2 and 1,2,3 cyclopropane tricarboxylic acid prepared according to the method of the present invention may be employed as synthetic lubricants either alone or in combination with various additives such as anti-oxidants, pour point depressors, viscosity improvers, dyes, extreme pressure agents, anti-corrosion agents, or other additives particularly adapted to tailor properties in the final product for particular use. The synthetic lubricants of the present invention may be blended with hydrocarbon lubricating oils, if desired, as well as with other synthetic lubricants. They may also be used as hydraulic fluids as well as in grease compositions.-

In preparing the compounds of the present invention,

a simple triester such as the triethyl ester of cyclopropane tricarboxylic acid -is first prepared. The reaction is more W specifically described in the example which follows:

EXAMPLE 1 92 gm. of metallic sodium were added. After the sodium had. reacted, 320 gm. of ethyl m-alonate was added drop wise with rapid stirring. After the ethyl malonate was added, the solution was refluxed at 78 C. during the slow addition of 520 gm. of ethyl A,'B, dibromopropionate. After the addition of the bromoester was complete, the mixture was stirred and refluxed for 7 hours. Excess ethanol was distilled oif and 600 cc. of water added. The reaction mixture was transferred to a separatory funnel and the desired product extracted from the water-ethanol mixture by repeated ether extraction. The extracted product was dried over 50 gm. of anhydrous magnesium sulfate. The extract was filtered and the ether removed from the filtrate by distillation. The final product, triethyl 1,1,2-cyclopropanetricarboxylate, was recovered by distilling at a reduced pressure. The triester boiled at 110-118 4 mm. Hg.

55 gm. of the triethyl 1,1,2-cyclopropanetricarboxylate was placed in a 2,000 cc., three-necked flask, together with 312 gm. of Z-ethyl hexanol and 4.6 gm. of metallic sodium. The 312 gm. of 2-ethyl hexanol represented a molar ratio ofalcohol to triester of 11 to 1. The mixture was heated with stirring under a Snyder fractionating column until 22 cc. of ethanol was collected. The solution was cooled and approximately 700 cc. of toluene was added as diluent. The mixture was then washed with water, dilute HCl, and again washed with water. Toluene and excess 2-ethylhexanol were removed by distilling at reduced pressure with the final triester product being obtained by distillation in a molecular still. The product boiled over a temperature range of 32125 C. at 33-34 microns of mercury. The boiling range indicates a mixture of mono-, di-, and tri-substituted ethyl ester, as well as a small amount of unreacted triethyl ester. The properties of this mixed ester of cyclopropane tricarboxylic acid are as follows:

Following the method set forth in Example 1, 55 gm. of triethyl-1,1,2-cyclopropanetricarboxylate was esterified with 447 gm. of lauryl alcohol. To the reaction mixture 4.6 gm. of sodium was added. The mixed lauryl-ethyl ester product recovered boiled over a temperature range of 110160 C. at 32 microns mercury. The properties of this product follow:

Acid No--- 1.46 Sap No 163 Vis. cs. at-

100 F 25.07 '210" F 5.28 V.I 150 Pourpt, F +50 Flash pt F 500 Fire pt., F 555 EXAMPLE 3 Following the method of Example 1, a mixed triester of cyclopropane tricarboxylic acid was prepared by reacting 55' gm. of triethyl- 1,1,2-cyclopropanetricarboxylate with 283 gm. of ethylene glycol n-butyl ether in the presence of 4.6 gm. of sodium. The product recovered had the following properties:

Acid No Sap No Vis. cs. at

V.I 108 Pour pt., F 60 Flash pt., F Fire pt., F

EXAMPLE 4 Following the procedure described above, 55 gm. of triethyl-1,1,2-cyclopropanetricarboxylate was reacted with 614 gm. of heptadecanol in the presence of 4.5 gm. of sodium. The recovered product, a mixed heptadecyl EXAMPLE 5 Into a 500 ml. B-necked, round bottom flask, fitted with a stirrer, condenser and thermometer, 165 gm. of ethylbrornoacetate is placed. 2 gm. of sodium is added during which a vigorous reaction takes place. Temperature during the addition is maintained between 1-20-130 C. After the initial reaction subsides an additional 21 gm. of sodium is slowly added. Thereafter the reactants are heated for an additional three hours; The product is taken up in ether and water washed to remove the salt formed during the reaction. The final product is recovered after the removal of ether by distillation at reduced pressure. The triethyl 1,2,3 cyclopropanetricarboxylate obtained boils altto C. at 9 mm, Hg.

55 gm.-of the triethyl ester is then placed in a 2000 cc. 3-necked flask together with 312 gm. of Z-ethylhexanol and 4.6 gm. of sodium. The mixture is heated with stirring under a Snyder fractionation column until approximately 25 cc. of ethanol is distilled off The ester is then washed free of sodium 'alcoholate and a final prodnot recovered by distilling at reduced pressure. The desired product boils over a fairly wide range indicating a mixture of mono, di and tri substituted ethyl esters of 1,2,3 tricarboxylic acid.

EXAMPLE 6 EXAMPLE 7 In amanner similar to the method described in Example 5, a mixed triester jof 1,2,3 cyclopropanetriboxylic acid is prepared by reacting 5.5 gm. of triethyl 1,2,3 cyclopropanetriboxylate with 47.5 gm. of n decyl alcohol. To the reaction mixture 0.5 gm. of sodium is added. The mixture is heated and after recovery of the theoretical amount of ethanol a final triester product is recovered by distilling at reduced pressure.

EXAMPLE 8 To 5.5 gm. of triethyl 1,2,3 cyclopropanetricarboxylate, prepared according to Example 5, 39 gm. of 2,2-dimethylpentanol is added in the presence of 0.5 gm. of metallic sodium. After reaction, as previously described, a product mixed dimethylpentyl-ethyl esters is obtained by distilling at reduced pressure.

EXAMPLE 9 Following the procedure set forth in Example 1, a trimethyl ester of cyclopropanetricarboxylic acid was prepared by reacting -153 gm. of methyl-bromoacetate with approximately 20 gm. of sodium at a temperature of about 120 to 150 C. The mixture is heated for a period of approximately three hours after the sodium is added. The product is taken up in ether water washed to remove the sodium salt formed and distilled at reduced pressure.

4.6 gm. of the trimethylcyclopropanetricarboxylate obtained is reacted with 23.8 gm. of n-decanol in the presence of 4.6 gm. of sodium. The mixed ester product resulting is recovered by distillation, at reduced pressure.

EXAMPLE 10 4.6 gm. of the trimethylcyclopropanetricarboxylate prepared according to Example 9, is reacted with 39.0 gm. of a C Oxo alcohol in the presence of 4.6 gm. of sodium, according to the method previously described. The mixed triester product is recovered by distillation at reduced pressure.

EXAMPLE 11 Following the procedure set forth in the foregoing examples, a mixed triester is prepared by reacting 5.5 gm. of triethyl 1,2,3 cyclopropanetricarboxylate with 27.9 gm. of n-dodecanol and 23.8 gm. of n-decanol in the presence of 4.6 gm. of sodium. Recovery of the product provides a mixed ester of 1,2,3 cyclopropanetricarboxylate having alkyl groups of different chain length derived from the different alkanols used.

By this method a variety of mixed triesters of both the 1,1,2 and 1,2,3 cyclopropanetricarboxylate acids can be prepared.

As has been previously indicated, the synthetic lubricants of the present invention may be used alone or in conjunction with other synthetic lubricants or mineral oil lubricants. The separate esters of the new invention may be blended together to provide a mixed synthetic lubricant. Typical of the manner in which blended esters of the present invention may be used as lubricants is shown in the following table.

The properties of mixed blends of the esters of Examples, 1, 2 and 3 were prepared and analyzed:

The suitability of the new esters of the present invention as lubricants will be apparent from the data which follows in Table II. These data were obtained from wear tests carried out on the standard shell 4-ball testing apparatus. This test apparatus includes 3 rigidly held stainless steel (52-100 stainless) metal balls submerged in the lu bricant to be tested in a metal cup. A 4th steel ball of the same metal and size is placed into contact with the 3 fastened balls by a suitable loading arm and allowed to rub for a fixed period of time. The contact points on [70%, Ex. 1, Ester; 30%, Ex. 2, Ester] Applied Load Scar Diam- Neutral I eter mm. Min. Oil

20 kg 0. 666 0.86 Extreme Premsur Conditions:

Seizure Load, kg 75 55 1 At 60 kg. applied load.

As will be apparent from the wear data in Table II above, the synthetic lubricants of the present invention provide very satisfactory lubrication. Their high temperature stability, resistance to oxidation, low pour and high flash points make them particularly suitable for rigorous conditions.

While the invention herein has been described in considerable detail with respect to certain preferred improvements, it is to be understood that variations and modifications can be made which will fall within the scope of the invention described above and as defined in the claims which follow:

We claim:

1. A synthetic lubricant consisting essentially of a triester of the formula H wherein A and B are selected from the group consisting of H and COOR with the proviso that A is COOR when E is H and B is COOR when A is H; and R is a member of the group consisting of straight and branched chain alkyl groups having from 5 to 20 carbon atoms.

2. A synthetic lubricant consisting essentially of a triester of 1,1,2 cyclopropanetricarboxylic acid wherein the alcohol portion of the ester is a member of the group consisting of straight and branched chain alkyl groups having from 5 to 20 carbon atoms.

3. A synthetic lubricant consisting essentially of CH2 COOCHzCHzOC Hq C H9OCH2OH2OOCCH--C COOOHzCHzO 0,119 4. A synthetic lubricant consisting essentially of 14 29 C14H19000-g- O o o o 014E 5. A synthetic lubricant consisting essentially of C O O CnHzE 7 V 8" a, 7. A synthetic lubricant consisting essentially of 11. A synthetic lubricant consisting essentially of cm 2000061113 oncooeflms cflH130oo-oHo CIQH25OOC-4'CH CHCOOC1QHZ5 000061313 5 12. A synthetic lubricant consisting essentially of 8. A syntheticlubricant consisting essentially of G c00CwHn CH, CUOCHHW o1uH2,ooooH-0Hoooo 125 OIH"OOC ,CH G g I References Cited in the file of this patent 0000mm" UNITED STATES PATENTS 9. A synthetic lubricant consisting essentially of a tri- 2 857 309 Y Barthel 7 Oct 21 1958 ester of 1,2,3 cyelopropanetricarboxylic acid wherein the alcohol portion of the ester is a member of the group OTHER REFERENCES consisting of straight and branched chain alkyl groups having from 5 to 20 carbon atoms.

10. A synthetic lubricant consisting essentially of 15 Darapsky: Chem. Abst., 4, 2466 (1910). 

1. A SYNETHIC LUBRICANT CONSISTING ESSENTIALLY OF A TRIESTER OF THE FORMULA 